Fuse construction



6, W. -WlARD FUSE CONSTRUCTION Filed A ril 2;, 1943 -2 Sheets-Sheet l 5'. W Wzlard p l G. w. wmnb i 2,398,169

FUSE CONSTRUCTION Filed April 23, 1943 2 Sheets-Sheet 2 Patented Apr. 9, 1946 FUSE CONSTRUCTION George W. Wiard, Keswick, Va., assignor to Virginia Electric Manufacturing Corporation, Charlottesville, Va., a corporation of Virginia Application April 23, 1943, Serial No. 484,259

5 Claims.

This invention relates to electric fuses generally, and particularly to fuses of the knife blade type.

The principal object of the invention is the provision of a casing for enclosing the fuse link and supporting the knife blades, which shall normally hold the parts in rigid unity, but which may be readily disassembled to permit removal of the knife blades for the renewal of the link.

Another object of the invention is the provision of a fuse of the character described, with. provisions for ventilating the chamber of the casing.

A further object of the invention is the construction of the casing of plastic parts whereby advantage may be secured of the insulating qual ity of plastics in providing a shock-proof casing, and the versatility of plastics employed with respect to transparency and color, so that the barreel of the casing can be made transparent to render the fuse link visible, and the end caps, or one of them, provided with a distinctive color to indicate the rating of the fuse.

Still another object of the invention is the provision of a fuse of the. type described, having an indicator visible from outside the casing, in the form of a painted area which changes color responsive to heat variations within the casing, showing when the circuit is loaded and the fuse about to blow, and indicating a relieved condition of the circuit, this feature of the invention being particularly advantageous when direct view of the link is obscured by a filling of heat dissipating material within the casing chamber or where the casing is opaque.

Other objects of the invention will appear as the following description of several illustrative forms proceeds.

In the drawings which accompany and form'a part of the following specification and throughout the several figures the same characters of reference have been employed to designate identical parts:

Figure 1 is a longitudinal section through a fuse embodying the principles of the invention;

Figure 2 is a longitudinal section taken along the line 2-2 of Figure I;

Figure 3 is a cross-section taken along the line 3-3 of Figure I;

Figure 4 is a cross-section taken along the line 4-4 of Figure 1;

Figure 5 is a cross-section taken along the line 5-5 of Figure 1;

Figure 6 is a cross-section taken along the line 8-6 of Figure 1;

Figure '7 is a perspective view of the barrel showing the plug at one end in partially withdrawn position;

Figure 8 is a longitudinal section through a form of fuse in which the link is screwed or otherwise. detachably secured to the knife. blades;

Figure 9 is a longitudinal section taken along the line 9-9 of Figure 8;

Figure 10 is a known form of fuse link to the use of which the subject invention is adapted;

Figure 11 is a longitudinal section through a modified form of fuse;

Figure 12 is an end view of a modified form of plug useable alternatively with respect to the plug shown in Figure 1;

Figure 13 is a longitudinal section through a modified form of the invention showing the thermally responsive paint indicator.

Referring now in detail to the several figures, and first adverting to that form oi. the invention shown in the group of Figures 1 to 7, inclusive, the reference character I represents as a whole a fuse casing comprising a tubular barrel 2 which in the form shown is made of molded plastic with bands of screw threads 3 about its opposite ends. The ends of the barrel 2 are provided with closure plugs 4, each of which has a skirt 5 extending within the barrel 2 and snugly fitting the bore thereof, and a peripheral flange 6 which rests against the end of the barrel. Each plug is formed with a diametrical slot 1 shaped to snugly fit the respective knife blades 9 and H] which are inserted through said slots, and which project oppositely from the casing i, fuse link H is positioned longitudinally within the barrel 2' and in the illustrated form of the invention is soldered at its opposite ends to the knife blades 9 and 10. The inner ends of the plugs 5 are formed with recesses I! which lighten the plugs. The recesses are preferably of smaller diameter than the length of the slots 1, but are provided with diametricall opposite mortises forming depthwise continuations of the end portions of the slots 1, so that the knife blades are supported throughout the entire depth of the plugs, in the interest of maximum strength and rigidity. Figure 7 shows that the outer ends of the barrel 2 are formed with diametrically aligned notches l3, whichv as shown, are semicircular. The plugs 4 are each formed with diametrically disposed pin holes I which intersect the flange 6 at opposite points", forming semicircular notches IS in the lower faces of said flanges, so that when the plugs are in place the notches i3 and notches I 5 register, forming tubul'ar seats half in the barrel and half in the plug,

for the pins l6 which pass through the knife blades 9 and I0, through the pin holes in the plug with their ends resting within said tubular seats, thereby preventing rotation of the plugs. The ends of the casing l include ring nuts I! having the peripheral flanges [8 which overlie the plugs 4, and having side flanges l9 which screw upon the barrel 2 and overlie the ends of the pins [5. When the ring nuts are screwed tightly in place, they clamp the plugs tightly against the ends of the barrel and tightly clamp the ends of the pins (6 between said plugs and barrel. Thus, a rigid fuse assemblage is prvided.

The casing I may be made of any desired material. All parts, including the barrel 2, plugs 4 and ring nuts I! are preferably made of plastic. This has the advantage of being non-com ductive so that one may grasp the casing with immunity from shock. Another advantage of having the casing of plastic is obviation of the use of vital metal. A further advantage of plastics is that they may be readily made in various colors so that one or both of the ring nuts I! may be made of a distinctive color to indicate the rating of the fuse.

It is, however, within the purview of the invention to make the casing or any part thereof of metal or of any other suitable material.

It is contemplated that the chamber 20 within the casing 2 may be empty, surrounding the link II, in which case the condition of the link may be observed through the barrel, in the event that the latter is of transparent material, or filled with a heat dissipating powder or other form of substance as is customary in fuses. In the event that the chamber is empty, the heat generated by the electrical resistance of the link H, or by the blowing of said link may be dissipated by the ventilation of the chamber 20 through the provision of the grooves 2| formed in the walls of the slots I of both plugs com municating on the one hand with'the chamber 20, and on the other with atmosphere providing for circulation of air through the casing I.

In lieu of the grooves 2|, the plugs 4 may be provided with ventilating apertures 22, as shown in Figure 12.

In that form of invention shown in Figures 1 and 2, the link II is soldered to the respective knife blades 9 and [0 so that for the renewal of said link it is necessary for the user to disassemble the fuse casing, remove the knife blades with the remains of the fuse link, and return the same to the manufacturer for the replacement of the link. It is, of course, assumed that the user will have a replacement link and knife blade unit so that he can immediately reassemble the fuse. Herein is a saving of vital metal, for the same pair of knife blades can be repeatedly refurnished with new fuse links.

In Figures 8 and 9, the same construction of casing is disclosed as in Figures 1 and 2, but the fuse link and knife blade unit differs from that of the first described modification, in that the link is attachably secured to the respective knife blades by means such as the screws 23. Ihe replacement of the fuse link may be readily accomplished by the user, who merely unscrews the blown link and substitutes a similar replacement link. In order that the knife blades will be maintained spaced apart the proper distance while the replacement is being made, the links are connected by a fiber strip 24 which is suitably secured to the knife blades. In that form of the invention shown in Figures 8 and 9, the recesses l2 in the plugs 4 are of sufficient size to house the screw connections 23. In the event that it is desired to employ the standard form of link 25 shown in Figure 10 in place of the link ii shown in Figures 1 and 8, it is merely necessary to have the knife blades 9 and I0 extend further into the barrel 2 of the casing and to secure the link 25 by two screws passing through the slots 26 and 21.

In Figure 11 a slightly modified form of the invention is shown, in which the barrel 28 of the casing I has an integral end closure 29 at one end, slotted as at 30 to receive the knife blade ID. A pin 3! passes through a diametrical aperture through the integral end closure 29 and through an aligned hole in the knife blade iii. Inasmuch as the ends of the pin 3| are exposed in this form of the invention, it is preferred to make the pin of non-conductive material so as to avoid the risk of shock, in the event that the hand of the user comes into contact with the end of the pin while removing the fuse from or replacing it in the fuse box.

The construction of the casing i at the opposite end, and the pin means for securing the knife blade 9 are the same as in the hereinbefore described forms of the invention.

Figure 13 shows another modification of the invention in which a visual indicator is employed to show the condition of the fuse link with respect to load or overload. In this modification the link and knife blade unit and the casing are by way of example similar to that of the modification illustrated in Figure 1. The barrel 2 of the casing l is provided with a band 32 of paint having the characteristic of color change respon sive to variations in heat. If the barrel 2 is transparent, the painted band 32 may be on the inside wall of said barrel and visible therethrough. If the barrel is opaque, the painted band should be on the outside of said barrel. This type of indicator is good for a fuse, whether the chamber within the barrel 2 is empty or filled with heat dissipating powder, or whether the barrel be made of metal, plastic, fiber or any other material. When the fuse circuit is loaded, the heating of the link incident to the current passage therethrough is indicated by change in color of the paint. As the blowing point is approached, this is indicated by intensification of color change, If the load is relieved, the color changes back to the original shade. If the fuse blows, this is indicated by a still more intense color change. The painted band, as shown, surrounds the link in the zone of maximum heat, but it is within the scope of the invention to position the band at any other desired point. A paint composed of'iodid of copper and iodid of mercury in equal proportions, in a suitable binder such as gum arabic, is adapted for this purpose.

While I have in the above description disclosed what I believe to be preferred and practical embodiments of the invention, it will be understood to those skilled in the art that the details of com struction and the arrangement of parts as shown and described, are by way of illustration and not to be construed as limiting-the scope of the invention which is defined in the appended claims.

What I claim as my invention is:

l. Fuse construction comprising a tubular bar rel having diametrical notches across one end face thereof, a plug having a portion fitting into said barrel and a flange overlying the end of said barrel, said 'plughaving.adiamctrical pin hole therethrough intersecting the plane of the inner face of said flange forming diametrical notches in said inner face adapted to register with the notches in the end f said barrel, said plug having a closed end slot therethrough in a plane perpendicular to said pin hole, a replaceable fuse link unit comprising a fusible strip within said I barrel and a knife blade secured to the end thereof snugly surrounded by said slot and extending therethrough, said knife blade having a pin hole registering with the pin hole in said plug, a pin extending through said plug and knife blade having its ends seated in said matching notches, and a ring nut having an end portion overlying the flange of said plug and a flange surrounding the ends of said pin, said ring nut being screwed to said barrel by means of which the ends of said pin may be clamped between said plug and barrel.

2. Fuse construction as claimed in claim 1, the opposite end closure being integral with the barrel.

3. In a fuse, in combination, a link unit comprising a fusible strip secured in lapped relation to the adjacent portion of a knife blade, and a casing for said link unit comprising a barrel surrounding said fusible strip, a plug forming an end closure for said barrel having an inner portion fitting into said barrel and an outer flange overlying the end of said barrel, said plug having a bore at its inner end surrounding the joint between said fusible strip and knife blade, said plug having a slot through its outer end longer than the diameter of said bore, snugly embracing said knife blade, the wall of said bore having mortises extending to the inner end of said plug, being continuations of the end portions of said slot and closely embracing the inner lateral margins of said knife blade.

4. In a fuse as claimed in claim 3, said barrel having diametrical notches across the end face thereof and said plug having a diametrical pin hole therethrough intersecting the plane of the inner face of said flange forming diametrical notches in said inner face adapted to register with the notches in the end of said barrel, said knife blade having a pin hole therethrough registering with the pin hole in said plug, a pin extending through said plug and knife blade having its ends received in said matching notches, and a ring nut having an end portion overlying the flange of said plug and a flange surrounding the ends of said pin, said ring nut being screwed to said barrel and clamping the ends of said pin between said flange and barrel.

5. In a fuse a barrel having its ends terminating in parallel planes and having its end faces diametrically notched in a common longitudinal plane, a fuse link unit comprising a fusible strip within said barrel and knife blades secured to said strip projecting from the ends of said barrel, plugs forming closures for the opposite ends of said barrel comprising portions fitting within the barrel and outwardly extending end flanges contacting the respective end faces of said barrel and being provided with pin apertures therethrough forming diametrically opposite notches in the contacting faces of said flanges matching with the notches on the end faces of the barrel to form pin seats, said plugs being formed with end slots fitting said knife blades through which the latter extend, said knife blades being formed with pin holes in diametrical alignment with said pin apertures and pin seats, pins passing through said holes, apertures and pin seats, resting against the opposite end faces of said barrel, securing said plugs in place andpreventing endwise movement of said fuse link unit, and caps on the ends of said barrel enclosing the ends of said pins.

GEORGE W. WIARD. 

